How to automatically switch to camera view after entering preview mode
WARNING: If you are a 100% python person, and hate my answer already, leave now, because, yes, we are using logic bricks. 

You will need a "Scene" logic brick, on the "set camera" mode. Specify the camera and rig this to an "Always" sensor. 



This works in a pinch, but it gives some extremely strange perspective depths, and I wouldn't recommend using it for this reason. The real way is to hit Num0 every time. Exhausting, I know. 

Note: after further testing, it would appear that the weirdo bug is gone! :D I could be incorrect, but this would make this a valid method in releases 2.77-later at least. Happy blending.